State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources & Guangxi Key Laboratory of Sugarcane Biology, Guangxi University, Nanning, 530004, China.
Center for Genomics and Biotechnology, Haixia Institute of Science and Technology, Fujian Provincial Key Laboratory of Haixia Applied Plant Systems Biology, College of Life Sciences, National Engineering Research Center for Sugarcane, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
BMC Plant Biol. 2022 Jul 22;22(1):363. doi: 10.1186/s12870-022-03749-9.
Sugarcane is an important crop for sugar production worldwide. The Sugars Will Eventually be Exported Transporters (SWEETs) are a group of sugar transporters recently identified in sugarcane. In Saccharum spontaneum, SsSWEET13c played a role in the sucrose transportation from the source to the sink tissues, which was found to be mainly active in the mature leaf. However, the function and regulation of SWEETs in sugarcane remain elusive despite extensive studies performed on sugar metabolism.
In this study, we showed that SsSWEET13c is a member of SWEET gene family in S. spontaneum, constituting highest circadian rhythm-dependent expression. It is a functional gene that facilitates plant root elongation and increase fresh weight of Arabidopsis thaliana, when overexpressed. Furthermore, yeast one-hybrid assays indicate that 20 potential transcription factors (TFs) could bind to the SsSWEET13c promoter in S. spontaneum. We combined transcriptome data from developmental gradient leaf with distinct times during circadian cycles and stems/leaves at different growth stages. We have uncovered that 14 out of 20 TFs exhibited positive/negative gene expression patterns relative to SsSWEET13c. In the source tissues, SsSWEET13c was mainly positively regulated by SsbHLH34, SsTFIIIA-a, SsMYR2, SsRAP2.4 and SsbHLH035, while negatively regulated by SsABS5, SsTFIIIA-b and SsERF4. During the circadian rhythm, it was noticed that SsSWEET13c was more active in the morning than in the afternoon. It was likely due to the high level of sugar accumulation at night, which was negatively regulated by SsbZIP44, and positively regulated by SsbHLH34. Furthermore, in the sink tissues, SsSWEET13c was also active for sugar accumulation, which was positively regulated by SsbZIP44, SsTFIIIA-b, SsbHLH34 and SsTFIIIA-a, and negatively regulated by SsERF4, SsHB36, SsDEL1 and SsABS5. Our results were further supported by one-to-one yeast hybridization assay which verified that 12 potential TFs could bind to the promoter of SsSWEET13c.
A module of the regulatory network was proposed for the SsSWEET13c in the developmental gradient of leaf and circadian rhythm in S. spontaneum. These results provide a novel understanding of the function and regulation of SWEET13c during the sugar transport and biomass production in S. spontaneum.
甘蔗是全球制糖的重要作物。新近在甘蔗中鉴定出的糖将最终被输出载体（Sugars Will Eventually be Exported Transporters，SWEETs）是一组糖转运蛋白。在甜高粱中，SsSWEET13c 参与了蔗糖从源到汇组织的运输，其主要在成熟叶片中活性较高。然而，尽管对糖代谢进行了广泛的研究，但 SWEETs 在甘蔗中的功能和调控仍不清楚。
本研究表明，SsSWEET13c 是甜高粱 SWEET 基因家族的成员，构成了最高的昼夜节律依赖性表达。它是一个功能基因，当过量表达时，可促进拟南芥根伸长和增加鲜重。此外，酵母单杂交实验表明，20 个潜在的转录因子（TFs）可以与甜高粱 SsSWEET13c 启动子结合。我们将发育梯度叶片和昼夜节律不同时间以及不同生长阶段的茎/叶的转录组数据进行了组合。我们发现，20 个 TF 中有 14 个表现出与 SsSWEET13c 相对的正/负基因表达模式。在源组织中，SsSWEET13c 主要受 SsbHLH34、SsTFIIIA-a、SsMYR2、SsRAP2.4 和 SsbHLH035 的正调控，而受 SsABS5、SsTFIIIA-b 和 SsERF4 的负调控。在昼夜节律中，SsSWEET13c 在早晨比下午更为活跃。这可能是由于夜间糖积累水平较高，受 SsbZIP44 负调控，受 SsbHLH34 正调控。此外，在汇组织中，SsSWEET13c 也积极参与糖积累，受 SsbZIP44、SsTFIIIA-b、SssbHLH34 和 SsTFIIIA-a 的正调控，受 SsERF4、SsHB36、SsDEL1 和 SsABS5 的负调控。我们的结果还得到了一对一酵母杂交实验的进一步支持，该实验验证了 12 个潜在的 TF 可以与 SsSWEET13c 的启动子结合。
提出了一个调控网络模块，用于研究甜高粱叶片发育梯度和昼夜节律中 SsSWEET13c 的功能。这些结果为 SsSWEET13c 在甘蔗中糖运输和生物量生产过程中的功能和调控提供了新的认识。
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